Is it true that the more anger and fear is present, the more danger there is that life force energy depletion can lead to death of a spirit and also physical humans?

This is true as well. It is a simple but an accurate description of the state of being at an extreme on the dark end of things. When spirits who have turned away from the light use up their energy, they will in fact disperse to the extent they lose their integration, and this is their demise. So the energy will be absorbed into the universe and re-utilized at some point, but is no longer theirs to continue their existence. For a physical human at an extreme low ebb, when all the thoughts are dark and no opening is available for Creator’s love to come in, the individual can, in like fashion, fade and pass away. At that point, the physical body may no longer support them and they must transition. This is the worst possible circumstance to begin a transition back to the light because in a state of extreme depletion, it is unlikely they will be able to perceive the light callers and then will be trapped in the lower astral plane and things will worsen from there.